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Sensors & Actuators for Robotics

23RIPC210

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Module 4: Specialized Sensing in Robotics

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Electrochemical sensors, Potentiometric sensors, Thermochemical sensors, Humidity and

moisture sensors, Radiation sensors, Microwave sensors.

Textbook 1: 8.3-8.8,9.3,9.4

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Textbooks:

1.Nathan Ida, Sensors, Actuators, and Their Interfaces A multidisciplinary introduction 2nd Edition,2020, IET, Control, Robotics and Sensors Series 127.

2.D. Patranabis, Sensors and Transducers, PHI Learning Pvt. Ltd.

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Photoelectric sensors �

  • Photoelectric sensors operate based on the photoelectric effect, where light energy is converted into electrical signals.
  • When photons (energy = hf) strike a material surface, their energy is transferred to electrons.
  • Electron emission occurs only if the photon energy exceeds the work function of the material.
  • This process can be understood as a collision between photon and electron, releasing the electron when sufficient energy is provided.
  • Devices such as photomultipliers and photoelectric cells utilize this principle for sensing applications.
  • These sensors are among the earliest and most fundamental optical sensors developed.

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Photoelectric sensors �1.The photoelectric sensor �

  • Photocathode is made of low work-function material → enables easy emission of electrons.
  • Incident light causes electron emission, which are accelerated toward the photoanode due to applied potential difference.
  • The resulting current is proportional to light intensity.
  • Quantum Efficiency:
    • Number of electrons emitted per photon
    • Depends on photocathode material
  • Materials Used:
    • Metals (low efficiency)
    • Cesium-based materials (high efficiency, wide spectral response: UV to IR ~1000 nm)
  • Construction:
    • Enclosed in vacuum or low-pressure noble gas (argon)
    • Gas enhances gain via ionization collisions
  • Advanced Technology (NEA surfaces):
    • Uses cesium-coated semiconductor
    • Operates at lower voltage compared to classical sensors
  • Note: Traditional sensors require high operating voltage (hundreds of volts).